LONDON — Prime Minister Tony Blair has been questioned by police investigating allegations that government honors, such as seats in the House of Lords, were bestowed in return for political contributions, Blair’s office said Thursday.

Downing Street said Blair was not interviewed as a suspect in the case, but it is still extremely rare for a serving prime minister to be questioned by police.

Police have been investigating claims that all three major political parties awarded seats in the House of Lords and lesser titles such as Member of the Order of the British Empire in return for secret loans.

Campaign funding rules allow those who offer loans — but not donations — to remain anonymous.

The Labour Party has said it accepted, but did not disclose, loans of almost $25 million from 12 supporters. The opposition Conservative and Liberal Democrat parties have acknowledged they have also received secret loans.

Several senior figures in the Labour and Conservative parties have been questioned.

Blair has been forced to acknowledge some supporters who offered the loans were later nominated for seats in the House of Lords.

His office said that during the interview, which lasted more than 90 minutes, the prime minister explained why he had nominated certain individuals for government honors.